1. Field of the Invention
The present invention relates to a process of producing a highly homogeneous cellulose solution. More particularly, the present invention relates to a process of producing a highly homogeneous cellulose solution, in which a mixture of powdered cellulose with polyvinyl alcohol powder is fed in conjunction with concentrated NMMO (N-methylmorpholine N-oxide) into a kneader or an extruder to produce a highly homogeneous cellulose solution, or into the kneader connected with an extruder to produce a swollen cellulose/polyvinyl alcohol paste and the paste thus produced is moved into the extruder at a higher temperature than the kneader to produce a highly homogeneous cellulose solution.
2. Description of the Prior Art
It is known that cellulose has a very high affinity with other substances but is insoluble in many solvents owing to a chain structure having strong intramolecular and intermolecular hydrogen bonding. Among solvents used to dissolve cellulose, NMMO is most widely used.
Because of advantages that pollutants are not generated because a used solvent is completely recovered and recycled, and finished products have high mechanical strength, a process of producing cellulose fibers using such a NMMO solvent is usually applied to a process of producing products comprising cellulose, as suggested in U.S. Pat. No. 3,447,935.
Various processes of producing such cellulose fibers have been proposed. For example, U.S. Pat. Nos. 4,142,913, 4,144,080, 4,196,282, and 4,246,221 disclose processes of producing cellulose fibers, in which cellulose is swollen in a NMMO aqueous solution containing 50% or less moisture, and water is vacuum-distilled from the NMMO aqueous solution having swollen cellulose to produce spinning liquid and the spinning liquid is extruded into the cellulose fibers.
However, these processes are disadvantageous in that physical properties of the cellulose fibers are readily reduced owing to thermal degradation because a long time is consumed from a dissolution step of cellulose to a spinning step of cellulose, and production cost of the cellulose fibers is increased because energy is excessively consumed.
Further, WO 94/06530 discloses a process of producing a cellulose solution by removing moisture using a thin film distillation device, but it is disadvantageous in that the device is complicated and not suitable to produce a highly viscous cellulose solution.
Furthermore, U.S. Pat. No. 4,221,574 suggests a process of producing cellulose fibers, in which liquid tertiary amine oxide containing 5 to 15 wt % moisture is used as a solvent, and a cellulose sheet is swollen at 65 to 95xc2x0 C. and heated with agitation to be spun. However, this process has a disadvantage in that a nonhomogeneous cellulose solution is obtained because of a film formed on a pulp sheet.
Meanwhile, according to U.S. Pat. No. 4,416,698, solid NMMO is used instead of liquid NMMO, and the solid NMMO and a cellulose pulp are agitated in an extruding device and the resulting mixture is spun, but this process is disadvantageous in that the amount of undissolved particles is large in a solution because a great amount of the solid NMMO and cellulose pulp powder is used in the process, and so mass production of the cellulose pulp is hard to accomplish.
In addition, WO 97/47790 proposes a process of producing cellulose fibers, in which fibril-typed cellulose powder used instead of cellulose pulp sheet and a high concentration NMMO aqueous solution, containing 5 to 20 wt % moisture, with a temperature of 50 to 130xc2x0 C. are mixed in an extruder with twin screws to be spun. However, this process is disadvantageous in that production cost of the cellulose fibers is increased because the number of replacable filters for removing undissolved particles and impurities is increased during spinning of cellulose, and physical properties of the cellulose fibers are reduced because a great amount of undissolved particles prevents a cellulose solution from being uniform.
Moreover, a process of producing a cellulose solution is provided by U.S. Pat. No. 4,416,698 and WO 97/47790, in which a mixing, a swelling (paste), and a dissolving step are conducted in an extruder, but this has a disadvantage of not sufficiently dissolving cellulose in a solvent.
Therefore, it is an object of the present invention to avoid the above disadvantages, and to provide a process of producing a highly homogeneous cellulose solution, having advantages in that a vacuum distillation step is not needed to remove water owing to use of a concentrated NMMO aqueous solution, the highly homogeneous cellulose solution is obtained without a separate swelling step in an extruder, and a cellulose fiber with excellent resistance to fibrillation is produced by using such homogeneous cellulose solution.